如何在文本文件中找到重复的行并进行打印？

如何在文本文件中找到重复的行并进行打印？

这很容易做到：

with open('file') as f:    seen = set()    for line in f:        line_lower = line.lower()        if line_lower in seen: print(line)        else: seen.add(line_lower)